feat: add tests and update mds

ui-tui/src/__tests__/messages.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, it } from 'vitest'
+
+import { upsert } from '../lib/messages.js'
+
+
+describe('upsert', () => {
+
+  it('appends when last role differs', () => {
+    expect(upsert([{ role: 'user', text: 'hi' }], 'assistant', 'hello')).toHaveLength(2)
+  })
+
+  it('replaces when last role matches', () => {
+    expect(upsert([{ role: 'assistant', text: 'partial' }], 'assistant', 'full')[0]!.text).toBe('full')
+  })
+
+  it('appends to empty', () => {
+    expect(upsert([], 'user', 'first')).toEqual([{ role: 'user', text: 'first' }])
+  })
+
+  it('does not mutate', () => {
+    const prev = [{ role: 'user' as const, text: 'hi' }]
+    upsert(prev, 'assistant', 'yo')
+    expect(prev).toHaveLength(1)
+  })
+})